<!DOCTYPE html>
<html>

<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel="stylesheet" href="../bootstrap-5.1.3-dist/css/bootstrap.css">
    <script src="../bootstrap-5.1.3-dist/js/bootstrap.js"></script>
</head>
<style>
    div {
        width: 200px;
        height: 50px;
    }
</style>

<body class="container">
    <!--mx-auto设置<h3>水平居中，mb-4设置<h3>底外边距为1.5rem-->
    <h3 class="mb-4 mx-auto border border-primary" style="width:150px">mx-auto</h3>
    <!--ms-4设置左外边距为0.5rem-->
    <div class="ms-2 border border-primary">ms-2</div>
    <div class="border border-primary">正常的盒子</div>
    <!--ms-4设置左外边距为1.5rem-->
    <div class="ms-4 border border-primary">ms-4</div>
</body>

</html>